You should check out my scenario here http://greenfootgallery.org/scenarios/648 It uses single pixel actors, but in a unique and fast way It could also be expanded to incorporate multiple materials.

You can jump levels with the 1 button And pressing I gives you invincibility And if you click while holding M, Zony will jump to your mouse :)

Check the source, is it the places where the block is a 1? Because those are invisible walls that only enemies react to. There are some right outside the main entry room... weird :/

Oooh! Fluid simulations! I had a working one a while ago, but i didn't upload it. I might refine it a bit and upload it later. As for speed, how are you determining the physics for a particle? For my physics, i had If it can fall, fall if it cant fall, move randomly to an open adjacent space.

Where were these walls? By translucent do you mean transparent? I searched all through level 1 and i couldn't find a single wall that i could walk through. In other levels there are walls that you can walk through and act as secrets, but none in level 1, and they are never at a slight angle.

The elevator problem has been fixed with this new upload, but the sword slider thing is actualy quite difficult to 'fix', as it would mean isolating both the top and bottom half of the animation. I'll see what i can do.